Koehler has dealt with some discomfort for a couple of days, which is why Miami opted to call up lefty Justin Nicolino from Triple-A New Orleans to face the Reds in the middle of the three-game set at Cincinnati.
"It's all right, just locked up on me a little bit," Koehler said. "Thought we would play it safe."
The fear was Koehler would take the mound, and not work deep into the game. So instead of taking that risk, Nicolino, the Marlins' No. 3 ranked prospect, was brought in to make his Major League debut.
"We're fortunate to have a guy like Justin to come in here and fill in," Miami manager Dan Jennings said. "He's earned this. He's been Pitcher of the Year in the Midwest League, in the Florida State League, Southern League. He's putting together a nice year this year."
Koehler has been incredibly durable since his first year of professional baseball, which was 2008. He's never been sidelined at any level due to injury.
The Marlins initially promoted Koehler to the big leagues in 2012. Last year, he made all 32 of his scheduled starts and logged 191 1/3 innings.
Koehler, 5-4 with a 3.76 ERA this season, has appeared in 14 games with 13 starts.
How long Nicolino remains with the club will hinge on a number of factors, including his performance. If Koehler is better in the next few days, that will be part of the equation.
The organization also is weighing what to do with Jarred Cosart, who has a rehab assignment start set for Double-A Jacksonville on Sunday. Cosart, recovering from vertigo, could rejoin the rotation, depending on how he is throwing.
And on July 2, Jose Fernandez (Tommy John surgery) is expected to join the rotation.
• First baseman Michael Morse (right ring finger) is continuing to get his timing down at Double-A Jacksonville. He went 2-for-3 on Friday night, and on Saturday he was scheduled to get more at-bats as a designated hitter.
The finger issue had bothered Morse long before he went on the DL.
"He was in pain, there is no doubt about that," Jennings said. "He was trying to fight through and swing through some pain. Now, the discomfort has subsided. He's basically back in Spring Training mode, getting his timing back."
• Reliever Bryan Morris (lower back strain) will begin his rehab assignment on Sunday with Advanced Class A Jupiter.